Control moment gyroscopes provide directional control for a variety of orbiting vehicles, for example, spacecraft. Control moment gyroscopes normally include a motor for spinning the rotor about a rotor axis, a gimbal wherein the rotor is supported or suspended, a gimbal torque motor for rotating the gimbal about a gimbal axis, and a control system. The control moment gyroscope is fixedly mounted to the orbiting vehicle. During operation of the control moment gyroscope with the rotor either mechanically supported by bearings or magnetically suspended within the gimbal, the rotor is spun about the rotor axis at a predetermined rate. The gimbal torque motor rotates the gimbal and spinning rotor about the gimbal axis which is perpendicular to the rotor axis. The rotor is of sufficient mass and is spinning at a rate such that any movement of the rotor outside its plane of rotation will induce a significant torque about an output axis which is normal to both the rotor axis and the gimbal axis. This torque is applied to the orbiting vehicle for providing directional control thereof.
Magnetically suspended rotors within the control moment gyroscopes are utilized to overcome mechanical disturbance problems and short-life problems associated with a mechanically supported rotor. The magnetic suspension system within the control moment gyroscope utilizes various magnetic actuators to levitate the rotor within the gimbal. Any magnetically suspended control moment gyroscope must have a back-up system in case the magnetic suspension system fails. Generally, this back-up system, also referred to as a touchdown system, takes the form of mechanical bearings for supporting the rotor. This touchdown system prevents damage to the various magnetic actuators levitating the rotor and other components in the event of power loss or magnetic suspension system failure by preventing contact between the rotor and the various magnetic actuators.
One common touchdown system consists of a mechanical radial bearing coupled to the gimbal of the control moment gyroscope and through which a shaft member extends from the rotor. Adequate clearance is provided between the shaft and the radial bearing inner diameter to allow for normal function of the magnetic suspension system. Should the magnetic suspension system fail to operate, the shaft contacts the inner diameter of the radial bearing before the rotor contacts the magnetic actuators, thus preventing damage to the magnetic actuators. An axial thrust bearing is added to the radial bearing to prevent excess axial excursions.
In addition to a touchdown system for preventing damage to the magnetic actuators in the event of an inoperative magnetic suspension system, a launch-lock system is necessary during launch of an orbiting vehicle. When the magnetic suspension system is not energized during launch, normal operating clearances provide an unacceptable opportunity for the magnetically suspended rotor within the gimbal to move or rattle about therein. Allowing the rotor to move or rattle about within the control moment gyroscope leads to high-impact loads thereon and damage thereto during launch vibration. In addition, if the magnetic suspension system failed during operation, the rotor would be free to move or rattle about within the control moment gyroscope for the remainder of the mission of the orbiting vehicle. Such movement and rattling about causes significant shock and vibration whenever the orbiting vehicle moves. Therefore, in addition to a touchdown system for preventing damage to magnetic actuators in the event of power loss or other magnetic suspension system failures, a launch-lock system is required to support the rotor during launch and during operation if the magnetic suspension system fails.
Most mechanically supported control moment gyroscopes take the launch vibration loads through bearings supporting the spinning rotor and therefore do not require a separate launch-lock system. When launch-lock systems are used, they usually take the form of a device that clamps hardware to a structural member by means of an actuator. Common actuators used for such clamping function include pyrotechnics, paraffin actuators, solenoids, and motors. Such common launch-lock techniques would be heavy and complex when utilized with a magnetically suspended control moment gyroscope wherein the rotor is quite massive in order to provide a large torque output.
A need is present for innovative touchdown systems and launch-lock systems in order to save weight and complexity. In addition, a system for integrating the touchdown system and the launch-lock system for saving weight and complexity within the control moment gyroscope is apparent.